Process for treating contaminated earth

ABSTRACT

The invention comprises a process for treating contaminated earth with different organic and inorganic substances, such as for example benzene, toluene, naphthalene, phenols and other mono- and polycyclic or aliphatic oxygen-, nitrogen- and sulphur-containing hydrocarbon compounds as well as simple and complex inorganic or organic salts. The invention concerns a combination of the following processing stages: (a) homogenization and comminution of the contaminated earth with an addition of treated recycled water to obtain a pumpable suspension; (b) treatment of the suspension in a single- or multi-stage extraction process in counter-current with warm or hot recycled water according to the principle of increased dissolving power at high temperatures (over 100° C.) and at the corresponding pressure above the vaporization point; (c) drying of the suspension taken from the extraction systems until a residual humidity of less than 30% by weight approximately is obtained; and separating the dissolved substances contained in the recycled water (extraction agent) by cooling according to the principle of reduced dissolving power.

FIELD AND BACKGROUND OF THE INVENTION

The invention relates in general to contaminated earth treatment and inparticular to a new and useful process for the treating of contaminatedearth by homogenizing and comminuting the material and adding water andthereafter treating the water suspension by drying it and separatingdissolved substances.

According to the invention contaminated earth, in particular earth fromcoking plants or plants with similar products is treated. This earth isusually contaminated with various anorganic and organic substances, suchas benzene, toluene, naphthalene, phenols and other mon- and polycyclicor aliphatic oxygen-, nitrogen- and sulphur-containing hydrocarboncompounds as well as simple and complex inorganic or organic salts.

From German OS No. 32 16 771 a process for the cleaning of earthcontaminated with toxic material is known, wherein the earth is e.g.heated in a rotating drum and the resulting gas products are burnt.

German patent application No. P34 47 079 also refers to a process forthe thermal treatment of contaminated earth. Herein the earth is treatedat a temperature cf at least 600° C. and the resulting gas is alsoburnt. In the two cited processes, the gas contaminants are removed fromthe earth by means of thermal treatment at relatively high temperatures.For this purpose a relatively large amount of energy is required.

German Os No. 25 31 732 describes a process for the removal, treatmentand regeneration of oil-polluted earth. Herein the oil and thewater-soluble noxious components are washed out in low surface tensionwater preferably at temperatures between 60° and 90° C. Herein thecomminuted material to be treated is intensively mixed with the cleaningmedium in a spiral drum and then separated from the pollutant-bindingcleaning medium by sedimentation in a clearing sump.

A similar process for the regeneration of earth, contaminated inparticular by oil is known from German OS No. 27 24 271. Herein thecontaminated earth is suspended [slurry] possibly after comminution, ina liquid, e.g. water and then heated to vaporizing temperature in acontinuous flow chamber. The upper layer of the suspension is strippedoff and separated in the continuous flow chamber. It has been proventhat the substances dissolved are not washed out from the contaminatedearth in such a process at the vaporization temperature of water.

SUMMARY OF THE INVENTION

The invention provides a process for the treatment of contaminatedearth, wherein the complex thermal treatment at a temperature of atleast 600° C. can be omitted and a homogenization and comminuting of thetreated substances is carried out and the resultant material is formedinto a suspension with water in a subsequent extraction process.

The process according to the invention has the following advantages withregard to the described known processes:

1. Compared to thermal processes (combustion or pyrolysis) attemperatures of 600° C. and above, less energy from outside is required.

2. During the treatment of the liquid and gas contaminant less noxiousmatter is generated during the partial oxidation (POX) above 1200° C.,while during pyrolysis and combustion hazardous substances, such asdioxines and furanes, can be generated.

3. The revitalization of the treated earth is simpler compared to thesintering and klinkering of the earth in the thermal processes.

4. The remaining C-contents of the earth treated in the extractionstages is considerably smaller than in the case of pyrolysis of theearth at temperatures of more than 600° C.

5. Simple solvents, such as water, can be employed.

6. There is the option of using a membrane process for the treatment ofthese waters and the generation of pure water for the final treatment ofthe contaminated earth.

12. The combustion of the pollutant-rich residual gas of the POX, inaddition to the POX, serves for energy recovery and the CO₂ forming canbe used in the carbonization stage.

Accordingly, it is an object of the invention to provide a process forcontaminated earth which comprises homogenizing and comminuting thecontaminated earth to form a dissolved portion, adding recycled water tothe discharge portion to form a suspension which is contaminated withanorganic and organic substances, treating the suspension in anextraction system with at least either warm or hot water to form anextraction, and drying the extraction and separating the dissolvedsubstances from the cycle water.

A further object of the invention is to provide a process in which thesuspension is further treated and countercurrent with the cycle water atleast in one stage and at a temperature in the range of from around 120°to 180° C. and a pressure 8 to 12 bars and drying the extraction to anapproximate residual humidity of from 30% by weight and separating thesoluble substances from the cycle water by means of a condensation.

A further object of the invention is to provide a process for treatingcontaminated earth which is to carry out and is relatively inexpensiveand may be carried out in a simple apparatus.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects obtained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich preferred embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic diagram of a process flow system constructed inaccordance with the invention; and

FIG. 2 is a view similar to FIG. 1 showing additional process stepspossible with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The contaminated earth 1 is comminuted in a homogenizer 2 and thentreated cycle water 3/22 is added to obtain a suspension 4 (up to 300g/l).

In an extraction system or extractors 5 and 6 (multi-stage) thehomogenized earth suspensions 4 and 9 are treated with cycle water 7 and11 in a counter-current. The operational parameters are in particular:

    ______________________________________                                        Temperature        t   140 to 180° C.                                  Pressure           p = 8 to 12 bar                                            Acidity            pH = 8 to 9                                                ______________________________________                                    

A liquid phase 8 and solid phases 9 and 10 form in the respectiveextractors 5 and 6, so that so-called separation effects occur. The useof mechanical elements (agitators) or appropriate counter-currentcascades ensures that the solid phase remains a free-flowing suspension.

In the secondary extraction 6 the suspension 9 is aftertreated withso-called pure water 11.

In a drier system or dryer 12 (drum or belt dryer) the earth isseparated from the residual water until a residual humidity of less than30% by weight is obtained.

In a further homogenizer and agitator 15, a biomass (humus or such like)is admixed with the earth 14 and then the mixture is stored in aso-called maturity or activated earth dump 17. After a certain period oftime the earth 14 is available again as treated earth 18.

The physical process of hot-water extraction is expected to yield aremoval of harmful substances of 95% or more. The remainder (mainlyhydrocarbons without tied on [bound] S-, O- or N-atoms) of 5% or lesshas to be dealt with by the microorganisms of the activated earth dump.Anorganic electrolytes, which e.g. form during hydrolysis from therespective hydrocarbons, can also be removed from the cycle by means ofreverse osmosis.

As the residual contamination of the earth consists mainly ofhydrocarbons, these residues can be degraded by known, selectivelyworking means.

The charged hot water or liquid phases 8 and 26 of the extraction 5 isthen condensed and thus the dissolving power is reduced. The condensator27 may comprise a one-stage or a multi-stage process, so that differentoil-fractions 32 can be drawn off from the following separators 30 ifnecessary.

For the setting of the alkali-aluminate-silicate contents of thehot-water 8 an additional carbonization stage or carbonizer 24 can beinserted, where e.g. by means of CO₂ -containing flue gas 28 a part ofthese substances at liquid phase 25, e.g. Al₂ O₃, SiO₂, which usuallyhave the form of colloid solutions, is precipitated. These substancesare admixed with the earth, e.g. in the drier 12.

The oily phase with its sulphur-, oxygen- nitrogen- andhalogen-containing harmful substances 32 is then transformed into theresidual gases 42, 45, 48, 51 CO and H₂, H₂ S, HCl, HF etc. by means ofO₂, hot air 41 or a mixture of O₂ and air in the partial oxidationprocess (POX) 40 at temperatures of 1200° to 1400° C. Resultingby-products, such as HCL, H₂ S, COS and traces of NH₃ and HCN could beremoved from the cracked gas by means of known processes.

Then the gas is burnt. The energy 44 recovered in the condenser 43 fromthe waste heat of the residual gases 42 of the POX 40 and during thesecondary combustion (53) serves for the additional heating 19 and 20 ofthe water which flows in lines 11 and 7 of the extractors 5 and 6 and/ordirectly as an actuation of mechanical devices.

If necessary, steam with H₂ S, NH₃ and HCN at line 35 are separated fromthe hydrous phase 31 in a stripper 33 with the addition of direct steam34. A part of the cycle water from the stripper 33 is supplied to thehomogenization process through the line 21 and 22 or to the extractionstage 5 through the line 23 as cycle water. The other part of the cyclewater 36 is recycled as so-called pure water, this is effected by meansof the membrane separation process cross-flow filtration and/or reverseosmosis in a separator 37. The concentrate 38 is admixed with the cyclewater once the saline solution 47 has been separated in a halogenabsorber 46. Or, the concentrate 38 can also be admixed with the oilyphase of the POX 40 as a moderator. The pure water obtained after thereverse osmosis 37 is preferably led to the final extraction stage 6over the line 11. The surplus water 39 is either transferred out of thesystem or it is heated up direct coder by means of the exhaust gas 48 ofthe halogen absorber 46 and then used as heated water 50 for theextraction stages 5 and 6 and then either admixed with the untreatedcycle water 3 or added to the concentrate 38 before the halogen absorber46.

In the secondary combustion 53 the residual gases 51 are afterburnedonce air 52 and vapors 35 from the stripper 33 are added. Excess heat 44is extracted from the flue gases 54 before they are released into theatmosphere, the excess heat serving for the heating of water 19 and 20.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

I claim:
 1. A process for treating contaminated earth, comprisinghomogenizing and comminuting the contaminated earth to form a dissolvedportion, adding cycle water to the dissolved portion to form asuspension which is contaminated with anorganic and organic substancesby treating it in countercurrent with said cycle water in at least onestage system at a temperature in the range of approximately from 120° to180° C. and a pressure of from 8 to 12 bars using at least one of warmand hot water in order to form an extraction, drying the extraction,separating of dissolved substances form the cycle water, said suspensiondrawn from said extractor being dried to an approximate residualhumidity of 30% by weight, and separating soluble substances from thecycle water by means of condensation.
 2. A process according to claim 1,wherein the extraction is carried out at a temperature in the range offrom 140° to 180° C.
 3. A process according to claim 1, wherein a freeflowing suspension is maintained in said extraction by means ofmechanical elements.
 4. A process according to claim 1, wherein theextraction is carried out to a last extraction stage and the suspensionis after treated with pure water generated by means of reverse osmosis.5. A process according to claim 1, wherein the dried earth ishomogenized and a bio-mass preferably humus earth is admixed with it andthe resulting mixture is then stored in a maturing or activated earthdump.
 6. A process according to claim 1, wherein the residual harmfulsubstances remaining in the earth are removed by microorganisms.
 7. Aprocess according to claim 1, wherein the heated water obtained afterextraction is condensed in one of several stages for separation ofdifferent oil fractions.
 8. A process according to claim 1, wherein forthe purpose of setting an alkali-aluminate-silicate content of theheated water drawn from said extractor, a part of each of thesesubstances which are usually in the form of colloid solution isprecipitated by means of a CO₂ containing flue gas.
 9. A processaccording to claim 1, wherein an oily phase separated from the hot waterwith its sulphur-, oxygen-, nitrogen- and halogen-containing harmfulsubstances is transformed into CO, H₂, H₂ S, HCl, and HF in a process ofpartial oxidation by means of O₂ hot air and a mixture of O₂ and air ata temperature of from 1200° to 1400° C.
 10. A process according to claim9, wherein the resulting gas is burnt after having been purified from H₂S and halogen by washing.
 11. A process according to claim 9, whereinthe energy from the waste heat is used for the heating of the extractionstages.
 12. A process according to claim 9, wherein the cycle water istreated by means of cross flow filtration and reverse osmois to yieldpure water which is used for the final extraction and whose excess istransferred out of the system.
 13. A process according to claim 9,wherein a concentrate of a reverse osmosis is mixed with an oily phaseseparated from the hot water so that they can be transformed together.